The present invention relates to an apparatus and method for measurement of permeability or strain in permeable materials.
Permeability of a material can be defined as a rate of which a fluid flows through the material. The measurement of the permeability of materials, for example concrete, is of importance in determining the suitability of the material for various purposes such as fluid containment and structural life. Changes in permeability with stress presents a method of measuring strain in permeable material.
Generally, the known methods of measurement of permeability measure a change in pressure of a gas applied to the material and/or depth of liquid penetration in the material. This method is known as the pulse test method. This method takes a substantial time to run and may involve the preparation of special samples. For example, the contemporary construction industry relies heavily on laboratory tests carried out on samples taken during a pour of a large concrete slab or structure to ascertain the strength of the concrete for further construction to be carried out. A steady state test method is a another, more desirable, method and is employed in the current specification. Further, the steady state test method is practical for the measurement of strain. In situ testing is a further desired attribute to reduce time taken and cost. U.S. Pat. No. 4,979,390 describes one method and apparatus for testing relative permeability of materials. In general terms, this requires the application of a partial vacuum to a small test area on a piece of concrete and measuring the rate of decay of the vacuum to provide an index of permeability. A limitation of the method and apparatus described is that it is restricted to a measurement of relative permeability and only a single test surface of relatively small area.
International Application No PCT/AU94/00325 (WO 94/27130) Tulip Bay discloses a monitoring apparatus that can be used to detect faults or cracks in the surface of or within a structure or component. The monitoring apparatus described includes a substantially constant vacuum source connected in series with a high impedance to fluid flow device that in turn is connected with one or more minuscule flaw sensing cavities formed on the surface of or within a structure. A differential pressure transducer is connected across the high impedance device to monitor the vacuum state of the minuscule flaw sensing cavity or cavities. A pressure differential transducer monitors the change in vacuum condition between the minuscule flaw sensing cavities and the constant vacuum source. Accordingly, if there is a change in vacuum condition in the cavities which can arise from the formation and propagation of a crack, the change is detected by the transducer. Cracks of a length down to 250 micron have been detected using a constant vacuum source of only 200 KpA below atmospheric reference.
The apparatus in Tulip Bay is particularly well suited to incorporation in embodiments of the present invention. Accordingly the contents of Tulip Bay are incorporated herein by way of reference.
It is an object of the present invention to provide a simple, low cost in situation, method and apparatus for providing a measurement of the permeability of a material. It is a further object to provide a means of method and apparatus for measuring strain in permeable material by means of change in permeability with applied stress.
According to the present invention there is provided an apparatus for providing a measure of the permeability of a material including at least:
a substantially constant fluid pressure source;
at least one fluid impervious means for juxtaposition with the material in a manner to define, between said means and said material a corresponding fluid flow cavity;
a high fluid flow impedance means providing high impedance fluid communication between said pressure source and said fluid flow cavity;
sealing means for juxtaposition with the material and the fluid impervious means to define a fluid impervious region between said fluid flow cavity and a free surface of the material; and,
means for measuring steady state differential pressure across said high fluid flow impedance means to provide a measure of the permeability of said material.
Preferably said sealing means includes a seal that seals a peripheral edge of said article at a surface of said material and extends from the peripheral edge to define said fluid impervious region.
Preferably said at least one fluid impervious means includes a planar article for placement on said material.
Preferably said at least one fluid impervious means includes a sleeve disposed in a blind hole formed in the material, the sleeve extending for a portion of the length of the hole from the surface of the material and having a down-hole end spaced above a bottom of the hole, the sleeve forming a seal against an interior surface of said portion of the length of the hole, wherein said corresponding fluid flow cavity is defined between the down-hole end of the sleeve and the bottom of the hole.
Preferably said apparatus further includes a fluid impervious blank of a diameter less than the diameter of the hole and of a length less than a remainder of the length of the hole between said down-hole end of the sleeve and the bottom of the hole, said blank deposited in said hole prior to the insertion of said sleeve.
According to the present invention there is provided an apparatus for providing a measure of permeability of a material including at least:
a substantially constant fluid pressure source;
at least one first fluid impervious means each for placement on the material to define, between each first means and said material, a corresponding first fluid flow cavity;
first high fluid flow impedance means providing high impedance fluid communication between said pressure source and said first fluid flow cavities;
first sealing means for juxtaposition with the material and said first fluid impervious means to define respective fluid impervious regions between said first fluid flow cavities and a free surface of the material;
at least one second fluid impervious means each for placement in respective holes formed in said material in a manner to define, between said second means and a bottom of said holes, a corresponding second fluid flow cavities;
second high fluid flow impedance means providing high impedance fluid communication between said pressure source and said second fluid flow cavities;
second sealing means for juxtaposition with the material and the second fluid impervious means to define respective fluid impervious regions between said second fluid flow cavities and said free surface of the material; and
means for measuring steady state differential pressure across said first and second high fluid flow impedance means to provide a measure of the permeability of said material.
According to the present invention there is also provided a method for obtaining a measure of the permeability of a material including at least the steps of:
providing a substantially constant fluid pressure source;
coupling said constant fluid pressure source through respective high fluid flow impedances to one or more fluid flow cavities formed on/or in the material;
forming respective fluid impervious seals on/or in the material about each fluid flow cavity to define corresponding fluid impervious regions between each fluid flow cavity and a free surface of the material; and,
monitoring measuring steady state differential pressure across said high fluid flow impedances to provide a measure of permeability of the material.
According to the present invention there is also provided an apparatus for providing a measure of strain in a permeable material, said apparatus including at least:
a substantially constant fluid pressure source;
first and second fluid impervious means for juxtaposition at different locations with said material in a manner to define, between said means and said material, corresponding first and second fluid flow cavities;
first and second high fluid flow impedances providing high impedance fluid communication between respective first and second cavities and said pressure source;
said first cavity coupled in series at a first node to said first high fluid flow impedance, and said second cavity coupled in series at a second node to said second high fluid flow impedance;
sealing means for juxtaposition with the material and said first and second fluid impervious means to define a fluid impervious region between said first and second cavities and a free surface of said material; and,
means for measuring steady state differential pressure across said first and second nodes to provide a measure of strain in said material.
According to a further aspect of the present invention there is provided a method of obtaining a measure of strain of a material, said method including at least the steps of:
providing a substantially constant fluid pressure source;
coupling said constant fluid pressure source through respective first and second high fluid flow impedances;
forming first and second fluid flow cavities on or in said material;
forming respective fluid impervious seals on/or in said material about said first and second fluid flow cavities to define corresponding fluid impervious regions between each of said fluid flow cavities and a free surface of said material;
coupling said first high fluid flow impedance in series at a first node to said first cavity;
coupling said second high fluid flow impedance in series at a second node to said second cavity; and
measuring steady state pressure differential across said first and second nodes to provide a measure of strain in said material.
In one embodiment, said high impedance includes a very long length of small bore duct which allows a minuscule flow of fluid.
In an alternate embodiment, said high impedance comprises a permeable material such as sintered glass, an orifice or point restriction such as a needle valve being considered far too impracticable due to the minuscule flow required.
The magnitude of the high fluid flow impedance should be sufficiently high as to produce significant pressure drop across the high impedance in response to minuscule flow through the high impedance.